Electrical discharge device



1949 w. T. ANDERSON, JR 2,4773% ELECTRICAL DISCHARGE DEVICE Filed Sept. 11, 1946 SECT. A-A

FIG. 2 FIG. 3

SEC-T. a-e

FIG. 6

INVENTOR. WILLIAM T. ANDERSON JR.

ATTORNEY Patented July 26-, 1949 urrah rarest! OFFICE ELEQTEEIQAL DISCHARGE DEVICE New Jersey Application September 11, 1946, Serial No. 696,114

3 Claims. l

This invention relates to electrical discharge devices and is concerned in particular with metal vapor discharge devices,

High pressure metal vapor electric arc devices, as now commonly employed, comprise a discharge envelope constructed of fused quartz or high melting point glass, having an ionizable filling of metal vapor, and an inert gas, .e. g. argon, and a pair of cooperating incandescent electrodes, at least one ofwhich is an activated electrode. In such devices the inert gas serves as a starting gas adapted to give an initial discharge on imposition of an electrical potential on the electrodes sufiicient to ionize the gas, and the metal vapor serves to carry the arc discharge and is at a pressure such that the voltage consumption of the arc discharge is increased to at least double the voltage consumption of the discharge in the first moment after starting the discharge. Such devices are more particularly described'in Germer U. S. Letters Patent No. 2,202,199. The pressure of the metal vapor in such devices may thus amount to from about one-fourth of an atmosphere to several atmospheres and more, e. 3. about one atmosphere.

The efiiciency and life of metal vapor discharge devices depend in a considerable measure on the efliciency and life of the incandescent electrodes. It has, therefore, been aprlncipal object of the art to produce sturdy electrodes which do not disintegrate under the bombardment to which they are subjected by the current-carrying particles of the arc, principally by the positive gas ions. Many types of activated electrodes have, therefore, been developed as part of such high pressure metal vapor are devices, such, for example, as electrodes of coiled wires orthe like, e. g. in the form of a helix, of high melting metal, such as tungsten, combined in one form or another with highly emissive substances, e. g. barium, thorium or the like.

The purity of the inert gas of the ionizable filling is another important factor with respect to the usefulness of the discharge device. Thus, for instance, the electrical potential at which thesedevices will start depends in part on such purity. For this reason great precaution must be taken during the filling of the discharge devices to assure greatest possible purity of the inert gas and, therefore, getters, such as barium or phosphorus, are used, during the evacuation of the devices, for the purpose of binding any unwanted gases such as oxygen, nitrogen and hydrogen by chemical action and absorption;- since, however, such metals react at the high operating temperatures with silica and mercury, it is not possible to use them as an integral part of the finished device to bind such gases as hydrogen, nitrogen and oxygen as they are met with in the operation of the device as, for instance, remnants of such gases initially in the device or the gaseous filling or released from the quartz or glass envelope at high temperature or difiused through the envelope or the lead-in seals, such gases thus being free to contaminate therare gas filling with the result that the electrical potential required to start'the device is gradually increased until failure of the device occurs. Furthermoratraces of such gases as hydrogen and nitrogen tend to cause a decrease in the electron emissivity of the electrodes and to contribute to destruction of the electrodes. Hydrogen, for instance, reduces harmless oxides to form water vapor which on dissociation by the electric arc frees oxygen.

The oxygen then reacts with the leads and supports of the electrode to form metal oxide coatings which evaporate during the operation of the device and on deposition blacken the walls of the device, thus impairing the transmission of the visible and invisible radiations through the wall of the envelope. Positive nitrogen ions rapidly attack the electrode metal, e. g. tungsten, and the activation material, thus causing a decrease in the electron emission from such electrodes with resultant premature shortening of the useful life of the electrodes and therewith of the discharge device.

It is, therefore, one object of this invention to provide in high pressure vapor electric arc devices an activated electrode which shall have high electron emissivity combined with long life. It is another object of this invention to provide copious flow of electrons and simultaneously absorbing such gaseous impurities as hydrogen,.

nitrogen, and so forth. It is a still furtherv object of this invention to produce a metal vapor electrical discharge device as hereinafter described embodying at least one such incandescent electrode. Other objects and advantages of this invention will appear from the description thereof hereinafter following.

Referring to the drawings, forming part hereof, in which I have illustrated the nature of my invention:

Fig. 1 represents a cross-sectional view of an electrical discharge device with a pair of cooperating solid incandescent electrodes,

Fig. 2 represents an elevational perspective view, on an enlarged scale, of one embodiment of the electrode according to the invention,

Fig. 3 is a sectional view on the line A--A of Fig. 2,

Fig. 4 represents a sectional view like that of Fig. 3, but of a slightly different form of such embodiment,

Fig. 5 represents an elevational sectional view of another embodiment of the electrode according to the invention, and

Fig. 6 is a sectional view on the line BB of Fig. 5.

The electrical discharge device comprises the customary structural and operative elements of such devices, such as a discharge envelope of high fusing radiation transmitting material such as quartz or high silica content glass, an ionizable filling of inert starting gas, e. g. argon or noun or the like, and a discharge carrying metal vapor, e. g. vapor of mercury, cadmium, sodium, rubidium, arsenic or the like, electrical accessories such as energizing circuit, ballast etc., and so forth, and is characterized by the provision of at least one incandescent electrode according to this invention.

Referring to the drawings, I have shown in Fig. 1 a customary discharge envelope I, e. g. of fused quartz, of elongated tubular shape with cooperating incandescent electrodes 2 and 3, spaced apart at opposite ends of the discharge envelope supported by lead-in conductors 4 and 5 sealed through the discharge envelope.

The incandescent electrodes 2 and 3 consist of a composite body comprising on the one hand a high temperature resistant metal, e. g. tungsten. molybdenum or the like, or in some cases even nickel, iron or the like, as one member thereof, and on the other hand a metal of the group consisting of titanium, zirconium and hafnium. as another member thereof. The two members of this composite body are juxtaposed and are then subjected to a heat treatment to produce fusion thereof at at least part of the area of contact. The juxtaposition of the members of the composite body constituting the incandescent electrode according to this invention may be accomplished in any suitable manner. In Figs. 2 and 3 of the drawings I have illustrated one particularly effective way of achieving the desired result. In thiscase the electrode structure is in the form of a helical coil 6, each coil consisting of a stranded wire, one or more strands I consisting of high temperature resistant metal, e. g. tungsten, (indicated in Fig. 3 in light cross section) and one or more strands 8 consisting of metal of the group titanium, zirconium and hafnium, e. g. zirconium, (indicated in Fig. 3 in heavy cross section). In Fig. 4 I have shown another very effective electrode structure, comprising a stranded wire 9 of tungsten or other heat resistant metal having wound around it a helically arranged wire or ribbon ii! of metal of the group titanium, zirconium Fig. 6--are alternately superimposed, as for instance, disks ii of molybdenum or other heat resistant metal, as one member of the composite structure of the electrode, and disks l2 of zirconium or other metal of the group titanium, zirconium and hafnium as the other member of such composite structure of the electrode, the disks being superimposed upon each other for instance by being strung on a support l3, e. g. of molybdenum wire, which may simultaneously serve as lead-in and which may hold such disks together in firmly pressed contact by means of deformations [4 and IS. The disks, or washers, may have any suitable thickness, e. g. about 0.004 inch. Other structures adapted to produce close juxtaposition of the two members of the composite body, may be used, c. g. cones, cups, tubes or the like.

The'in'candescent electrode of the invention emits a copious flow of electrons. The electron emission emanates primarily from the fused junction of the two members of the composite body. Once the fused junction has been produced, ionization of the gaseous filling of the discharge device occurs on application of an electrical potential even when the electrodes are in an unheated condition and the gaseous discharge is quickly converted into a metal vapor arc. The production of the fused junction, at at least part of the area of contact, of the two members of the composite body may be accomplished in any desired manner by the application of heat. The fusion may be produced either as a special heating step, during or after the manufacture of the electrode structure, or as part of the heating occurring after scaling in of the electrodes during the evacuation of the discharge envelope. It is not necessary that the entire area of contact be fused since the heat developed during the operation of the device will produce whatever additional fused areas may be required during the life of the device. It may be noted that advantageously the fusion should take place by melting of the metal of the group titanium, zirconium and hafnium to the high temperature resistant metal, without melting of such high temperature resistant metal, so that in the preferred embodiment of the invention the temperature resistant metal has a melting point in excess of that of the other member. The high electron emissivity of the electrode of the invention is contingent on the heat treatment and the provision of the fused contact or junction area. Prior to the heat treatment, the electron emissivity is extremely low but once the fusion junction is produced the electrodes are adapted to emit a copious flow of electrons on application of an electrical potential. While the heat resistant or refractory metal has a relatively high work function and the metal of the group titanium, zirconium and hafnium has a relatively lower work function the composite electrode at the fusion junction has a work function lower than that of either component and, therefore, an electron emissivity higher than that of either component. The fusion area is produced by the fusion of one metal only. while the other metal remains solid, preferably by fusion of the metal of the group consisting of titanium. zirconium and hafnium.

In high pressure vapor are devices embodying one or more electrodes of this invention the metal vapor is preferably derived from a small quantity of the vaporizable metal and the vapor is at'such pressure duringdzhe operation of the device that the voltage consumption of the arc discharge is increased to at least double the voltage consumption of the discharge in the first moment after starting the discharge and, furthermore, all the vaporizable metal is preferably in the vapor phase during operation of the device so that the vapor density is maintained at a constant value.

The electrodes of the invention may be of socalled "self-heating" type, i. e. are operative on application of the electrical potential and without preheating and are admirably suited for use in connection with single in-leads, as shown in the drawings, although they may be used also in connection with double in-leads permitting, if desired, preheating of the electrode by resistance heating.

Titanium, zirconium and hafnium are extremely stable in air at lower temperatures, such as temperatures below 200 0., because of a thin sealing layer of oxide formed on the surface. At

t the operating temperature of the electrical discharge device, in excess of 900 (2., these metals have, however, in such'discharge devices a very high solubility for oxygen, nitrogen and certain other undesirable impurities but not for the rare gases or the metal vapor. The electrode thus binds, by absorption within its body, the undesirable gaseous impurities, with the result that the arcing potential of the discharge device is decreased and the impurities can not react with the tungstenor other like metal of the electrode.

Group -IV of the periodic system also includes thorium but while electrodes of tungsten and the like and thorium constitute activated electrodes as such they are not characterized by the essential feature of the electrodes of this invention in that they do not in the, operation of the discharge device dissolve oxygen and nitrogen or the like to any appreciable extent and the thorium does not, as do titanium, zirconium and hafnium, protect the. tungsten or the like from positive ion bombardment by these gaseous impurities.

The composite electrode of the invention is constructed preferably in such manner that the member comprising the heat resistant metal, e. g. one or more metals such as tungsten, molybdenum or the like, constitutes the major portion of the composite body and the member comprising metal of the group titanium, zirconium and hafnium constitutes the minor portion of the composite body, so that after the heat treatment the electrode of the invention exhibits a surface of heat resistant metal as well as a surface of the metal of the group titanium, zirconium and hafnium, thus avoiding a structure wherein, for instance, the zirconium substantially overflows and smothers the tungsten in itsentirety. In high pressure metal vapor discharge devices the most 6 through the envelope and impairs the over-all emciency of thedevice.

The incandescent electrode of the invention thus possesses great electron emission efficiency and withstands disintegration even in high pressure metal vapor arc lamps to a greater extent than has been achieved heretofore. It furthermore, promptly and continuously, during the life of the device in which it is embodied, dissolves oxygen, nitrogen and other undesirable gaseous impurities, thereby protecting the body of the electrode from destructive ionic gas bombardment and maintaining the lowest attainable breakdown voltage of the inert gas filling throughout the life of the device. Electrical discharge devices embodying such electrodes are thus easier to manufacture, are more eflicient in their operation and maintain their efliciency for longer periods of time than heretofore.

The electrode of the invention may also include in its composite body other elementswhlch may be desired. For instance, the electrode may thus include other activation materials, e. g., barium,

strontium or other highly electron emissive substance orsubstances, either in the form of a metal or a compound thereof, e. g. in the latter hafnium. Furthermore, the incorporation of such efiective electrodes according to the invention are those composed of tungsten or molybdenum or both as one member and zirconium as the other member, whereas in other devices, e. g. rectiflers, electrodes of iron or the like with zirconium or titanium orhafnium are quite useful.

Thus, electrodes of the invention make unnecsary the employment .of extreme precautions to avoid contamination of the'rare gas prior to and during the filling of the discharge device as has been necessary in the case of other incandescent 4 electrodes as heretofore known. The avoidance of premature disintegration of the electrodes also eliminates the undersirable deposition of sputtered particles of the electrode on the wall of the discharge envelope, a deposition which otherwise interferes with the transmission of the radiations other activation material will decrease the work function of the electrode still further, so that, where desired, the size of the electrode may thus be decreased, with resultant lower wattage loss and other benefits. Where, as for instance in the case of barium, such activation material has a relatively low vapor pressure the zirconium, titanium or hafnium member will protect such other activation material against easy vaporization, due to alloying of the two highly emissive substances with each other. The other activation material, i. e. the activation material dissimilar to titanium, zirconium and hafnium, may therefore be present in the electrode either as a separate element or,

advantageously, in alloyed form, such alloyed form being produced either initially or' during the operation of the device.v I may thus provide for instance an electrode in which the metal of the group titanium, zirconium and hafnium is alloyed with such other, dissimilar, activation of which consists of heat resistant metal and at least one strand of which consists of metal of the group consisting of titanium, zirconium and hafnium, said strands being fused together at at least part of the area of contact thereof to form a low work function fusion area.

. '2. An incandescent electrode comprising a plurality of superimposed disks, said disks consisting alternately of a heat resistant metal and a metal taken from the group consisting of titanium, zircomum and hafnium, said disksbeing fused to- 1 a gather along at least part 0! the areas of contact to form a low work function fusion area. REFERENCES CITED 3. An incandescent electrode comprising I; The following references are of record in the composite'body of at least one member of heat file of this patent: resistant metal and at least one member of metal rm taken from the group consisting of titanium, 811'- U STATES PATENTS conium and hafnium, said members being in Number N me Date closely juxtaposed conditioned fused together at 3,241,345 Gustin et a1. May 6, 1941 at least part of the area of contact to form a low 2,241,362 Gustin e a1 M y 1 work function fusion area, said electrode also 10 embodying an activation material comprising a FOREIGN PATENTS highly electron emissive substance other than Number Country Date titanium, zirconium or hafnium. 467,248 Great Britain Sept. 6, 1935 WILLIAM T. ANDERSON, Ja. 

